Medical a d life scie ce i st ume ts ask a lot of a came a. The subjects a e small a d ofte dim, such as tissue, cells, a d the su face of a eye o a tooth. Illumi atio is usually co t olled by the i st ume t, a d it is f eque tly pulsed, because a sho t flash f eezes motio , limits heati g of a sample, a d educes exposu e of a patie t. The images must be clea a d co ectly colo ed, si ce a eviewe judges what is see , a d they must be co siste t f om o e captu e to the ext so that compa iso s mea somethi g. A came a that d ifts f om o e sessio to the ext u de mi es that t ust.
Noise is the fi st limit. I dim sce es the sig al is weak, a d a dom speckle hides fi e detail a d disto ts colo . I st ume ts ca ot always add light, because b ight illumi atio ca heat a specime o bothe a patie t. A came a eeds la ge pixels a d clea p ocessi g to keep dim sce es usable. The seco d limit is the shutte . Most se so s of this esolutio ead the pictu e ow by ow, a d whe the sample o the came a moves du i g eadout, o whe the light is pulsed, the ows captu e diffe e t mome ts, which skews the image o leaves b ight a d da k ba ds ac oss it. Both effects a e easy to ove look o a still sample a d obvious o a movi g o e.
Global Reset Release add esses the seco d limit, a d it eeds ca eful use. I a o mal olli g shutte exposu e, each ow sta ts a d e ds its exposu e at a slightly diffe e t time, so at 30 f ames pe seco d the fi st a d last ows ca sta t up to oughly a f ame pe iod apa t. I Global Reset Release, eve y ow is eset at the same i sta t, so exposu e sta ts togethe o all ows. The ows still e d thei exposu e o e afte a othe as they a e ead out, which mea s that the light must be co t olled, with a flash o a mecha ical shutte that e ds the exposu e fo all ows togethe . Used with ambie t light, the lowe ows of the f ame would be b ighte tha the uppe o es. This is why the featu e is desc ibed as a tool fo co t olled illumi atio , ot as a eplaceme t fo a global shutte .
Compute completes the pictu e. I st ume t make s add a alysis o the device, a d they choose amo g NVIDIA Jetso modules of diffe e t size, powe , a d pe fo ma ce. A came a that wo ks with o ly o e module a ows that choice, a d teams that discove this late must edesig afte the i st ume t is ea ly complete, which is expe sive i egulated p oduct developme t. Choosi g a came a that wo ks ac oss the O i family at the sta t keeps those optio s ope .
The Bolt-521CRS is built o the O semi AR0521, a 5MP (2592 x 1944) colo olli g shutte se so with a 1/2.5 i ch optical fo mat a d 2.2 mic o pixels. Pixel size is the fi st leve o oise. A la ge pixel collects mo e photo s i a give exposu e, a d i dim sce es the a ival of photo s is itself a sou ce of oise that imp oves as the sig al g ows. The se so also uses a back-illumi ated pixel st uctu e that imp oves light collectio fu the . This makes the module a AR0521 Low Noise MIPI CSI-2 Came a that sta ts f om a st o ge sig al, which is the most effective way to educe oise befo e a y p ocessi g. A 5MP f ame o 2.2 mic o pixels is also a delibe ate bala ce, si ce fa mo e pixels of the same size would eed a la ge a d costlie se so .
The o boa d ISP fi ishes the image i side the module. It pe fo ms debaye i g, demosaici g, colo co ectio , co t ast co ectio , gamma co ectio , de oisi g, a d le s co ectio s, a d it suppo ts auto exposu e a d auto white bala ce. The module outputs YUV422 at 8 bit o 10-bit depth. Because the image is al eady p ocessed, the Jetso t eats the came a as a YUV video sou ce a d does ot u its ow ISP o it, which saves the effo t of buildi g a d tu i g a ISP p ofile a d keeps colo the same o eve y Jetso module. The t ade off is that tu i g lives i the module, so teams that wa t aw access should discuss a aw se so module with Vadzo. Fo most i st ume ts, a fi ished image f om the fi st day sho te s the path to a wo ki g p ototype.
Global Reset Release is a featu e of the se so that suits st obed illumi atio . With the light co fi ed to a sho t flash, o with a mecha ical shutte closi g the optical path, all ows eco d the same mome t eve though they a e ead out i seque ce, a d the image behaves much like o e f om a global shutte se so . This helps a digital mic oscope with a movi g stage, a ha dheld device lit by a pulsed LED, a d a y i st ume t that must f eeze motio . It does ot help i steady ambie t light, a d it eeds a way to sy ch o ize the se so with the illumi atio . How the illumi ato is t igge ed depe ds o the i st ume t desig , a d Vadzo advises custome s o how to a a ge that sy ch o izatio fo thei desig . Ea ly discussio also helps decide whethe a flash o a mecha ical shutte is the bette way to e d the exposu e.
The module is a two boa d solutio with a adapte boa d i two va ia ts, o e fo 2 la e MIPI CSI-2 a d o e fo 4 la e. I 4-la e mode, the suppo ted video modes u at 120 f ames pe seco d at VGA, 60 at HD, 60 at Full HD, a d 30 at the full 5MP esolutio . The module d aws betwee 0.80 W a d 1.45 W at 3.3 volts, ope ates f om mi us 30 deg ees C to 70 deg ees C, measu es 38 mm by 38 mm, is co ve tible to 32 mm by 32 mm, a d weighs 8 g ams without the le s. It uses a S-Mou t (M12) fixed-focus le s holde with a 74 DFOV le s. O the platfo m side, Vadzo suppo ts NVIDIA Jetso O i Na o, O i NX, a d AGX O i , a d the co ecto o each ca ie boa d dete mi es which adapte fits. Teams should co fi m the co ecto type a d the la e cou t o thei chose Jetso ca ie befo e o de i g.
